Multiple transport pathways for neutral amino acids in rabbit jejunal brush border vesicles.
Amino acids enter rabbit jejunal brush border membrane vesicles via three major transport systems: (1) simple passive diffusion; (2) Na-independent carriers; and (3) Na-dependent carriers. The passive permeability sequence of amino acids is very similar to that observed in other studies involving natural and artificial membranes. Based on uptake kinetics and cross-inhibition profiles, at least two Na-independent and three Na-dependent carrier-mediated pathways exist. One Na-independent pathway, similar to the classical L system, favors neutral amino acids, while the other pathway favors dibasic amino acids such as lysine. One Na-dependent pathway primarily serves neutral L-amino acids including 2-amino-2-norbornanecarboxylic acid hemihydrate (BCH), but not beta-alanine or alpha-methylaminoisobutyric acid (MeAIB). Another Na-dependent route favors phenylalanine and methionine, while the third pathway is selective for imino acids and MeAIB. Li is unable to substitute for Na in these systems. Cross-inhibition profiles indicated that none of the Na-dependent systems conform to classical A or ACS paradigms. Other notable features of jejunal brush border vesicles include (1) no beta-alanine carrier, and (2) no major proline/glycine interactions.
D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D004058:Diffusion; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D010649:Phenylalanine; D011392:Proline; D012964:Sodium; D008715:Methionine; D008239:Lysine; D000409:Alanine